Law enforcement and government intelligence agencies are big fans of using private sector data to conduct their operations. When such practices have run into constitutional and political barriers, agencies say they will back off, respect the Fourth Amendment, and get warrants.

But what happens when the warrants they seek are so broad they are little more than dragnets that scoop up and implicate the innocent? That’s behind the new wave of geofencing warrants, which are fueled with data coming from private companies that already gather loads of data for themselves and their advertisers. As the Guardian writes:

…privacy experts argue geofence and other broad warrants such as those that ask companies to sift through keywords people searched for are akin to a general warrant, made illegal by the fourth amendment right against unreasonable searches and seizures. Unlike other kinds of search warrants, which are targeted and seek information about people who law enforcement has probable cause to believe has committed a specific crime, these warrants don’t have a particular person in mind.

In other words, with reverse search warrants law enforcement is still looking for their suspect and they’re asking tech companies to give them a list of people to investigate. For geofence warrants, anyone in a certain place at a certain time becomes a suspect and is subject to further investigation which could mean giving police even more of their user data. For keyword search warrants, another relatively new mechanism to obtain user information that has emerged, anyone who searched for a certain phrase or address becomes a suspect.

Behind all these snares are the private companies hoovering up data on users every day:

It’s not just major tech players like Google and Facebook that are targets, however. Personal information in the hands of smaller companies that may not have the resources or wherewithal to withstand sweeping warrants is just as vulnerable, Cahn said. “You could subpoena period tracker apps to provide any users who apparently became pregnant during a given time period, for example,” he said.

“This information is flowing to so many different companies and vendors, even if you get one company trying to protect your location data you have so many more points of vulnerability in the commercial market than a decade ago,” Cahn said. “All it takes is one company to give up that information without a fight or more often than not sell it.”

Bottom line: the struggle to protect your Fourth Amendment rights never ends, and is getting even more difficult as we willingly share more information about ourselves online. Information governments and law enforcement can subpoena, or simply purchase (no warrant required).